In this article, we give a short overview of the theoretical background and properties of the unique polyoxovanadate K₆[V^IV ₁₅As₆O₄₂(H₂O)]·8H₂O (abbreviated V₁₅) containing a cluster of the fifteen V^IV ions and exhibiting layers of different magnetizations. Analysis of the magnetic and spectroscopic properties of this fascinating system constitutes a distinct trend in the study of complex nanoscopic polyoxometalates. V₁₅ cluster exhibits strong magnetic anisotropy closely related to the unquenched orbital angular momentum in the degenerate ground state. The degeneracy is interrelated with the spin frustration in V₁₅ which gives rise to a variety of interesting phenomena observed in this polyoxovanadate. We summarize the studies of the isotropic and antisymmetric exchange interaction and analyze its manifestations in magnetic properties, electron paramagnetic resonance, and inelastic neutron scattering spectra as well as in the spin-phonon relaxation in V₁₅. We briefly discuss also a long coherence time (Rabi oscillations) first discovered in molecular magnets due to which the V₁₅ cluster proved to be a prerequisite for the use of molecular magnets in quantum computing.